1. Field
One embodiment of the invention relates to a transmitter that transmits content, a receiver that receives content, and a content transmitting and receiving method.
2. Description of the Related Art
With widespread of computer networks such as broadband networks and wireless local area networks (LANs), digital information devices, digital home appliances, etc. having a communication function have been increasingly used. If a plurality of digital home appliances are connected to a network, the user can enjoy content via the network. The “content” refers to various types of digital data including, for example, MPEG-2 and MPEG-4 video data and audio data, document data such as text data and image data, and the like. Although content made up of such digital data can easily be copied without loss of quality, attention has to be paid to the issue of copyright of the content.
For example, in Japanese digital broadcasting services, it is defined that a total of up to ten contents received by a recorder through broadcast waves are allowed to be stored the internal device (see, for example, “The Association for Promotion of Digital Broadcasting,” “the Outline of Changes in the Dubbing 10 Rule,” on line, retrieved on Apr. 9, 2009, the Internet <URL: http://www.dpa.or.jp/images/news/dub10-outline.pdf>). Digital transmission content protection (DTCP) and digital transmission content protection over Internet protocol (DTCP-IP) are commonly used to output content from a transmitter to a receiver via an in-home network while protecting the content. As to DTCP, reference may be had to “Digital transmission Licensing Administer,” “Digital Transmission Content Protection Specification Volume 1 Revision 1.51,” on line, retrieved on Apr. 9, 2009, the Internet <URL: http://www.dtcp.com/data/info%2020071001%20DTCP%20V1%201p51.p df>). As to DTCP-IP, reference may be had to “Digital transmission Licensing Administer,” “DTCP Volume 1 Supplement E Mapping DTCP to IP, Revision 1.2,” on line, retrieved on Apr. 9, 2009, the Internet <URL: http://www.dtcp.com/data/info%2020070615%20DTCP%20V1SE%201p2. pdf>). Hereinafter, DTCP and DTCP-IP are both referred to as DTCP-IP. For example, Japanese Patent Application Publication (KORAI) No. 2008-165975 discloses a conventional technology in which authentication is performed between a stream recorder/player and another recorder to exchange a key for data scramble. Copy control information obtained when data is first recorded using the key is added to the data to be transmitted. After the data is recorded on the recording device, the data is deleted from an original storage medium.
According to DTCP-IP, content is accompanied with available number of times of dubbing. The available number of times of dubbing refers to the number of times content is allowed to be dubbed. For example, when content, which can be dubbed seven times, is dubbed from a transmitter to a receiver twice, the available number of times of dubbing managed by the transmitter is reduced to six after the first dubbing, and the content becomes available for the receiver. Further, the available number of times of dubbing managed by the transmitter is reduced to five after the second dubbing, and the content becomes available for the receiver. Such dubbings may be performed in parallel. However, as with the case described above, if the dubbing of the same content is performed a plurality of times, the transmitter is required to perform the dubbing of the same content a plurality of times. Consequently, transfer time increases according to the number of times of dubbing. Further, the storage capacity required of the receiver also increases according to the number of times of dubbing. This increases the amount of communication and resources for encryption.